Field of Invention
The present invention relates generally to the use of metallic nanoparticles to both enhance and spectrally modify the emission of excitable molecules, such as fluorophores, that being, both the shape and width of emission spectrum thereby causing a color change in emissions from the excitable molecules.
Description of Related Art
In the last 15 years, there has been a significant literature on metal-enhanced fluorescence (MEF), (1-4) where the near-field interactions of plasmon supporting nanoparticles with fluorophores typically give rise to spectroscopically favorable properties, such as enhanced fluorescence and a much improved system photostability. Most of the reports of MEF have focused on silver, due to its visible wavelength plasmon band and the subsequent ability to enhance fluorescence in the visible spectral region. Other metals have also been used to plasmon-enhance fluorescence, including gold, (5) copper, (6) Aluminum, (7) and Zinc. (8) Gold and copper nanoparticles typically enhance fluorescence in the red to near-IR region, while Aluminum and Zinc have particular advantages in the UV and visible spectral regions. Since the report of MEF from Zinc substrates by Geddes et al., (8) there have been numerous other reports. (9,10), However, in all these reports for Zinc and indeed, all of the metals, there has been virtually no reports of spectral distortions of fluorophores. Karolin and Geddes (11) recently demonstrated experimentally spectral shifts from copper substrates with Rhodamine 800 in the red spectral region(>700 nm), but there have been no reports in the UV or visible region to date. In addition, Le Ru has theoretically predicted spectral distortions, (12,13) although the fast-coupling and coupling from non-vibronically relaxed states would ultimately lead to blue-shifted emission spectra, which has not been experimentally observed to date either.
MEF has attracted significant research interest in recent years, from both a theoretical (14) and practical perspective (15-16) From a theoretical perspective, the mechanism of MEF is still under debate, but with significant progress made in the last few years, while the practical applications of MEF are widespread, including applications in imaging, e.g., tip-enhanced near-field optical microscopy, (17) high throughput analysis, (18) sensing and in the analytical and life sciences (19-20) to name but just a few.
In the vast majority of MEF studies, no spectral shifts or “distortions” are observed, with both the MEF and control sample spectra being reported as identical. Thus it would be advantageous to determine the level and amount of spectral shifts or distortions due to the proximity of different fluorophores to a variety of different metal nanoparticles.